There are various known methods for producing porous silica particles. For example, Japanese Unexamined Patent Application Publication No. S61-174103 discloses the method in which the colloidal solution containing primary particles (silica microparticles) with a mean particle diameter of 2500 Å or less is sprayed and dried using a spray drier, so that porous silica particles with a mean particle diameter of 1 to 20 μm are prepared.
Japanese Unexamined Patent Application Publication No. 2002-160907 discloses the method in which the colloidal solution is sprayed and dried to provide inorganic silica microparticle aggregates with a mean particle diameter of 1 to 100 μm including inorganic silica microparticles with a mean particle diameter of 2 to 250 nm. Then, this aggregate is coated with an oxide layer, so that spherical porous particles are made.
In addition, Japanese Unexamined Patent Application Publication No. 2010-138021 discloses making of the porous silica particles with a mean particle diameter of 0.5 to 50 μm and a specific surface area of 30 to 250 m2/g by spraying and drying the dispersion liquid containing silica microparticles of 10 to 50 nm. Japanese Unexamined Patent Application Publication No. 2010-138022 discloses making of the porous silica particles with a mean particle diameter of 0.5 to 50 μm and a specific surface area of 10 to 100 m2/g by spraying and drying the dispersion liquid containing silica microparticles of 50 to 300 nm. Japanese Unexamined Patent Application Publication No. 2005-298739 discloses making of the porous silica particles by spraying and drying the slurry containing the ceramic powder and the material which disappears due to the chemical reaction or the change in state occurring at a temperature of 40° C. to 250° C.
It has been generally known that cosmetics contain spherical porous silica particles and the like as the texture improver. For example, Japanese Unexamined Patent Application Publication No. 2009-137806 discloses the method of obtaining the powder solid cosmetic containing the porous silica particles to have the texture characteristics such as the smoothness, the moistness, the rolling effect, the even spreadability, the adhesive property, and the continuing rolling effect. These texture characteristics are typically required for the texture improver of the cosmetic.
However, it is concerned that the aforementioned porous silica particles might be categorized as the nanomaterial described below. In the announcement made by the European Commission as of Oct. 18, 2011, (1) the substances or materials containing particles for more than 50% in the number size distribution in the range of 1 to 100 nm, and (2) the substances or materials with a specific surface area (SA) per unit volume of more than 60 m2/cm3 are categorized as the nanomaterial. The aforementioned porous silica particles have both the nanometer-size pores and the large specific surface area. The specific surface area per unit weight converted at a silica density of 2.2 g/cm3 is more than 27 m2/g. It has not been verified that the particles categorized as the nanomaterial directly lead to the serious problem in environment, health, or safety but users and consumers will demand to avoid using the particles categorized as the nanomaterial.
If the definition of the nanomaterial is introduced to REACH in the future, it may be possible that the particles categorized as the nanomaterial cannot be used freely in the industrial use. It may be also possible that the submission of various kinds of documents for the use of the particles categorized as the nanomaterial is required. Therefore, the time and cost may be required in the procedure.